Hand-held power tools, such as circular saws, have been popular woodworking tools for many years. In a typical power tool operation, such as a sawing operation, the user begins by marking or otherwise identifying a desired line along which to saw the material to be cut. The user then guides the saw during cutting, manually aligning the blade with the desired line of cut. Maintaining this alignment manually can be difficult because the typical circular saw has a blade guard that obscures the user's view of the blade at the point of cutting, and thus impedes the user's ability to accurately align the blade with the desired cutting line.
To overcome this difficulty, one alternative has been to provide the circular saw with a guide slot. Typically located on the base of the saw, the guide slot is so aligned ahead of the blade in the forward cutting direction to provide a visual indication of the anticipated blade path through the workpiece. During operation, the user typically positions the saw so that the guide slot and thus the blade are aligned with the line of cut. This approach can provide a satisfactory cut, unless the saw blade is improperly aligned with the guide slot. A blade is typically oriented at a predesignated location on an arbor driven by the saw motor. Deviations from this orientation can occur causing misalignment between the blade and the guide slot. The guide slot will then incorrectly indicate the blade path, and the user relying on the guide slot will be less likely to cut the material as desired. Furthermore, since the blade is covered by the saw guard, the user cannot directly monitor the blade travel, and, therefore, may not detect the misalignment until substantial cutting has occurred. As a result, the workpiece may be ruined.
To overcome these limitations, another alternative has been to supply the saw guard with a transparent viewing window covering an aperture in the saw guard. Such a window enables direct observation of the saw blade as it enters the workpiece, which in turn enables the user to better maintain a desired cutting path. An extremely successful window can be found in U.S. Pat. No. 5,822,864, which is hereby incorporated herein by reference. This patent discloses a viewing window for covering an aperture in the guard of a hand-held circular saw. The window is movable between a closed position, wherein the window substantially covers the aperture, and an open position, wherein the window at least partially uncovers the aperture. The ability to at least partially uncover the aperture allows cleaning of the interior surface of the window if such interior surface becomes fouled by sawdust. This patent also provides for a structure to bias the window to a closed position.
It may be desirable in certain circumstances to provide a structure to lock the window in its closed position.